1. Field of the Invention
The present invention relates to an image sensor and a method for manufacturing the same, and more particularly, to an image sensor, which is capable of increasing the light-collection efficiency of a photodiode, and a method for manufacturing the same.
2. Description of the Related Art
Generally, an image sensor is a semiconductor device that converts an optical image into an electric signal. Among the image sensors, a charge coupled device (CCD) is a device wherein each metal-oxide-silicon (hereinafter referred as to MOS) capacitor is closely located and charge carriers are stored into the MOS capacitor and transferred. A complementary metal oxide semiconductor (hereinafter referred as to CMOS) image sensor employs CMOS technology that uses a control circuit and a signal processing circuit as peripheral circuits to form as many arrays of MOS transistors as the number of pixels, and adopts a switching mode that detects outputs sequentially. MOS transistors formed in the peripheral circuit as the same number of pixels.
In manufacturing such a variety of image sensors, there have been many endeavors to increase the photosensitivity of the image sensor. Among those endeavors to increase the photosensitivity, a light-collecting technique is the most important technique.
The image sensor generally includes photosensitive circuit parts sensing light and CMOS logic circuit parts transforming the light into electric signals and generating data. Recently, there have been many studies of light-collecting techniques by which the pathways of the incident lights injecting to the regions other than the photosensitive circuit parts are changed and collected in photodiodes that are photosensitive elements.
FIG. 1 is a cross sectional view showing an image sensor in accordance with a prior art, in which the main components of a conventional CMOS image sensor are directly related to light-collection are illustrated.
Referring to FIG. 1, the prior art image sensor includes a plurality of field insulating films 10 formed on a semiconductor substrate (not shown), at least one photodiode 12 which is an optical active region formed between these field insulating films 10, multilayer interlayer insulating films 14 and 18 insulating between layers of the top parts of the field insulating films 10 and photodiode 12 and a light shield layer 16 formed of metal or the like in the interlayer insulating film 18 in order to prevent incident light from being focused onto the field insulating films 10. An element-protecting film 20 is formed on the interlayer insulating film 18, and an interlayer insulating film 24 is formed on the element-protecting film 20. The color filter arrays 22a, 22b and 22c of red, green and blue are formed in the interlayer insulating film 24. A flattening layer 26 is formed over these color filter arrays 22a, 22b and 22c. Microlenses 28 are formed at the positions corresponding to the color filters 22a, 22b and 22c. 
As the materials of the color filters 22a, 22b and 22c of red, green and blue, mainly used are photoresists dyed in colors capable of absorbing only the light of a specific wavelength. As the materials of the microlenses 28, mainly used are polymer type resins.
The interlayer insulating films 14, 18 and 24 and the element-protecting film 20 are typically made by using silicon oxide films that are transparent insulating materials. The flattening layer 26 is made by using a photoresist in order to compensate for the roughness of the color filters.
In the constructed conventional CMOS image sensor, the incident light received via the microlenses 28 is separated into corresponding red, green and blue light through the red color filter 22a, green color filter 22b and blue color filter 22c. The separated red, green and blue lights are focused on the photodiode 12 at the positions corresponding to the color filters through the element-protecting film 20 and the interlayer insulating films 14 and 18, respectively. The light shield layer 16 arranged between the interlayer insulating films 14 and 18 plays the role of shielding the incident light so as not to deviate to other light pathways.
However, if the incident light on the photodiode through the microlenses 28 and the color filters 22a, 22b and 22c is not focused in parallel but focused to other light pathways, the photodiode 12 in the corresponding light pathway will be unable to sense the light or interference will occur with other adjacent photodiode 12. Such a phenomenon acts as noise in embodying a high performance image in a CMOS image sensor.